In a semiconductor device, performance improvement, such as improvement in operating frequency, has been strongly desired. However, in the semiconductor device, a series resistance between two main electrodes, through which an electric current mainly flows, impedes the performance improvement. Patent Document 1 describes the necessity of reducing the series resistance and, specifically, the necessity of substantially reducing a contact resistance between a semiconductor region and an electrode.
Patent Document 1 proposes to use, as a material of an electrode contacting an n+ silicon region, Er, Mg, Mn, Cd, Hf, Y, or Zr each having a work function close to −4.05 eV which is a work function of the n+ silicon region, and to use, as a material of an electrode contacting a p+ silicon region, Pd, Pt, Co, Ni, or Ir each having a work function close to −5.15 eV which is a work function of the p+ silicon region.
However, Patent Document 1 does not sufficiently clarify which of the above-mentioned materials is practically preferable. Further, according to the knowledge of the present inventors, oxygen is inevitably mixed into a silicide and a gate metal during heat treatment for silicide formation or the like at a contact portion. This results in a problem that an increase of a resistance of the contact silicide or the gate metal is inevitable.